1. Technical Field
This invention relates generally to information retrieval in a computer network. More particularly, the invention relates to managing references to embedded objects in a markup language (e.g., HTML, PGML, or the like) data stream.
2. Description of the Related Art
The World Wide Web is the Internet""s multimedia information retrieval system. In the Web environment, client machines effect transactions to Web servers using the Hypertext Transfer Protocol (HTTP), which is a known application protocol providing users access to files (e.g., text, graphics, images, sound, video, etc.) using a standard page description language known as Hypertext Markup Language (HTML). HTML provides basic document formatting and allows the developer to specify links to other servers and files. In the Internet paradigm, a network path to a server is identified by a so-called Uniform Resource Locator (URL) having a special syntax for defining a network connection. Use of an HTML-compatible browser (e.g., Netscape Navigator or Microsoft Internet Explorer) at a client machine involves specification of a link via the URL.
When the user of the browser specifies a link, the client issues a request to a naming service to map a hostname (in the URL) to a particular network IP address at which the server is located. The naming service returns an IP address that can respond to the request. Using the IP address, the browser establishes a connection to a server. If the server is available, it returns a Web page. To facilitate further navigation, a Web page typically includes one or more hypertext references known as xe2x80x9canchorsxe2x80x9d or xe2x80x9clinks.xe2x80x9d In HTML, each anchor is commonly delineated by a markup language xe2x80x9ctagxe2x80x9d set xe2x80x9c less than a href=xe2x80x9cpathnamexe2x80x9d greater than  less than /a greater than xe2x80x9d, where xe2x80x9cpathnamexe2x80x9d is the path information identifying the location of the linked page or object.
Recently, the computer industry has sought to add computer processing and communications capabilities to devices other than what would normally be considered a traditional computer. Such devices are quite varied and include, for example, personal digital assistants (PDAs), business organizers (e.g., IBM(trademark) WorkPad(trademark) and the 3Com(trademark) PalmPilot(trademark)), smartphones, cellular phones, other handheld devices, and the like. For convenience, these devices, as a class, are sometimes referred to as xe2x80x9cpervasive computingxe2x80x9d clients as they are devices that are designed to be connected to servers in a computer network and used for computing purposes regardless of their location. Pervasive computing clients, however, typically do not support the full function set of an HTML Windows-based client. As a result, transcoding services typically are required to translate information to be rendered on the pervasive client from one source markup language (e.g., HTML) to another markup language (e.g., PGML or Precision Graphics Markup Language, an XML-compliant language).
Markup language data streams typically include numerous references to embedded objects such as images, audio streams, video streams, applets, and other rich media content files. These references can occur anywhere in the markup language data stream, which is text data and is often quite complex. Rendering engines, such as browsers or viewers, process such data streams sequentially to ensure that elements in the stream are interpreted and rendered in the correct context. As a result, such engines cannot quickly discover the embedded references, but rather only identify the references when that part of the stream containing the object reference is parsed for rendering. Thus, it can take a significant amount of time before object references on these pages are discovered and processed. This delay results in slower interpretation and ultimate output of the markup language page content.
The present invention addresses this problem.
In accordance with the invention, a method for prefetching external resources required by a page returned from an origin server begins by processing a markup language data stream to determine whether the stream includes a list of external resources. If so, the routine processes the list and identifies at least one external resource to be prefetched. The external resource is then prefetched to the client rendering engine.
Preferably, the inventive prefetching method is implemented within a pervasive computing client having a rendering engine. The client may be connected to a transcoding proxy server. The proxy server preferably transcodes HTML returned from an origin server, which may be a conventional Web server, while generating the embedded object reference list.
By adding the list of references to external resources in a known place in the markup language data stream returned to the client, the proxy server makes it possible for clients to quickly determine which references are present in the stream. This determination can be made even before the entire data stream has been received at the client. As a result, and in accordance with the invention, a provisioned client, for example, may start one or more additional processing threads to retrieve those resources in parallel with the parsing of the rest of the stream. Thus, one or more resources are prefetched so that they may be available for immediate rendering when discovered during the actual parsing of the data stream that includes those object references.
It is another more general object of the present invention to enhance the processing of a markup language data stream at a client rendering device, such as a browser or viewer.
Still another object of the present invention is to enable a client rendering engine to prefetch given external resources identified in a page returned from an origin server.
Yet another object of the present invention is to provide a mechanism that prefetches external resources required by a markup language page data stream and that makes those resources available immediately when the page is parsed (and the object references to those resources are detected and actually requested).
The foregoing has outlined some of the more pertinent objects and features of the present invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the invention. Many other beneficial results can be obtained by applying the disclosed invention in a different manner or modifying the invention as will be described. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the following Detailed Description of the Preferred Embodiment.